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Heat Syncope

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Other Names

  • Heat Syncope
  • Orthostatic Dizziness
  • Postural Hypotension


  • This page refers to heat syncope, which can be defined as a transient loss or near-loss of consciousness due to the indirect effects of high ambient temperature




  • General
    • Characterized by loss of consciousness in hot environment and return to baseline following syncopal event
    • In addition to syncope, athletes of report dizziness, tunnel vision, pale or sweaty skin
    • Most commonly occurs following termination of exercise
  • Occurrences in sport
    • After standing for long periods of time
    • Immediately after cessation of activity
    • After rapid assumption of upright posture after resting or being seated
  • Misconception(s)
    • Heat syncope may be considered a misnomer, because heat does not directly cause syncope


  • General
    • Attributed to peripheral vasodilation, postural pooling of blood, diminished venous return, dehydration, reduction in cardiac output, and cerebral ischemia[1]
    • At the end of race, athlete stops moving, blood pools in lower extremities leading to syncope
    • Typically occurs during the first 5 days of acclimatization or in persons with heart disease or taking diuretics
  • Variant of postural hypotension[2]
    • Combination of volume depletion, decreased vasomotor tone and peripheral vasodilatation
    • Often precipitated by rapid change in position during exercise
    • Occurs in nonacclimatized patients during early stages of heat exposure, especially elderly

Associated Conditions

Risk Factors

  • Sports
    • Endurance events
    • Marathon
  • Environmental
    • Lack of acclimatization
  • Systemic
    • Cardiac disease
  • Medications
    • Diuretic use

Differential Diagnosis

Differential Diagnosis of Syncope

Differential Diagnosis Heat Illness

Clinical Features

  • History
    • Episode of fainting
    • Often associated with dizziness, tunnel vision, pale or sweaty skin
    • Often after cessation of exercise when venous pooling can occur in the lower extremities
  • Physical Exam
    • Pulse rate may or may not be diminished
    • Normal rectal temperature (for exercise, 36°C to 40°C [97°F to 104°F]
    • Following syncope, athlete should have a rapidly improving level of consciousness (15-20 minutes)


  • Primarily a clinical diagnosis in the right context
    • May require evaluation to exclude other causes if diagnosis unclear


  • Not applicable



  • General
    • Move the athlete to a shaded area
    • Monitor vital signs
    • Place the patient in a supine position, legs above the level of the head
    • Rehydrate
  • Hydration
    • Most athletes will do well with oral rehydration
    • Can consider IV fluid on a case-by-case basis


  • Transport to hospital
    • Some patients may require transportation to the hospital
    • Further workup should be pursued if failure to return to baseline
    • Transport should be considered for patients with high risk comorbidities

Rehab and Return to Play


  • No clear rehabilitation guidelines

Return to Play/ Work

  • No specific guidelines
    • Largely depends on athlete

Complications and Prognosis


  • General considered a self limited condition


  • Unknown

See Also


  1. Knochel J P. Environmental heat illness: an eclectic review. Arch Intern Med. 1974;133:841–864.
  2. Waters T. Heat Emergencies In: Tintinalli's Emergency Medicine: A Comprehensive Study Guide. 7th ed. McGraw Hill Medical. 2011: 1339
Created by:
John Kiel on 30 June 2019 22:49:56
Last edited:
20 September 2022 14:37:22